Giardia lamblia is a food and waterborne parasite prevalent in developing countries, and a major cause of outbreaks of diarrhea in the United Sates, that has been classified as a bioterrorism category B organism by the Center for Disease Control because compromised water and food supply could affect US populations as well as army units in foreign countries. Drugs commonly used against anaerobic protozoa are used to treat giardiasis. However, they produce undesirable side effects, clinical resistance may occur in both immunocompromised and immunocompetent patients, and the rate of recurrence is high. The goal of this project is to develop new drug targets for alternative treatments of giardiasis. The sequence of the G. lamblia genome is available, thus, a genomic approach combined with biological insight has been taken to identify enzymes essential for the survival of the organism that are absent or are sufficiently divergent from the human enzymes to exploit those differences in the design of inhibitors. The selected enzymes will be cloned and expressed in E. coli using high throughput techniques, and those that are expressed in soluble form will be validated in G. lamblia by transcription interference methods. Essential enzymes will be prepared for structural and functional studies. Crystal structures will be determined, and will serve to guide the design of inhibitors specific to the Giardia enzymes. Assays to determine the kinetic constants of the enzymes will be developed and the catalytic mechanism will be studied to facilitate the in vitro evaluation of the inhibitors. Crystal structures of enzyme/inhibitor complexes will reveal how the inhibitor may be further improved. The effect of the inhibitors on the growth of G. lamblia will be determined. The long range goals of the project is to establish a database of potential drug targets against giardiasis, to gain insight about their mechanism of action, and to prepare inhibitors that are ready for preclinical evaluation.